Electro-absorption modulators (EAM's) are a promising technology due to its small package size and its low drive-voltage, as well as its great potential for high degree opto-electronic integration to reduce the overall size of the transponders and transmitters in the wavelength-division multiplexing (WDM) fiber optic networks. As WDM optical networks increase rapidly in their size and complexity, wavelength tunability of the transponders and transmitters become desirable for inventory reduction, and for network management such as provisioning, dynamic provisioning and demand restoration in the optical layer.
The dominant light sources used in current WDM transmission equipment are the distributed-feedback (DFB) lasers with high average output power (13 dBm). While wide-band tunable lasers are becoming available with equivalent performance to that of DFB's, their cost-premium may hinder their wide spread adoption in the WDM networks. Although DFB only has tunability of a few nanometers by temperature, its low cost structure and its incumbent technology status call for a full exploration of its tunability before WDM equipment manufacturers opt for other more costly alternatives. EAM's are intrinsically wide bandwidth devices and have a packaged size typically a quarter of the competing technology. These devices are ideal modulators to work with DFB's in a number of applications, such as 8-channel 50 GHz-spacing transponders. Also, the main material system that the EAM modulators are built upon is Indium Phosphide (InP), which can be simultaneously used to build devices to generate, modulate, amplify and detect light at wavelengths used in WDM transmission systems. This commonality opens the door for high degree of integration, either by hybrid approach or eventually monolithically.